1. Field of the Invention
The present invention relates to a specimen holder used in an observation system, such as a transmission electron microscope. The invention also relates to the observation system and to a method of rotating a specimen.
2. Description of Related Art
A transmission electron microscope has a microscope column in which electron optics are positioned. In some instruments, a goniometer (goniostage) supporting a specimen holder used to hold a specimen is mounted in the microscope column. A specimen exchange chamber is mounted in a position opposite to the goniometer. In this case, this specimen exchange chamber is fitted with a transport device for transporting the specimen holder into the microscope column.
The structure of such a transmission electron microscope is schematically shown in FIG. 10, where the microscope or an observation system is generally indicated by reference numeral 1. This microscope 1 has an electron gun 14 for emitting and accelerating an electron beam 12, which is controlled by an illumination lens 2 and directed at a specimen 3. The specimen 3 is held on a specimen holder 4 which is supported by the support portion 5a of a holder support device 5.
The electron beam 12 directed at the specimen 3 and then transmitted through it is focused onto film 8 or image pickup means 13 consisting of a CCD camera 11 under control of an imaging lens 6. The image pickup means 13 can take and record a transmission image created from the specimen 3 by the electron beam 12. A fluorescent screen 7 is placed off the optical axis of the beam 12 during imaging.
The electron gun 14, illumination lens 2, holder support device 5, and imaging lens 6 are positioned in the microscope column 15. A specimen exchange chamber 9 is mounted at a side of the microscope column 15 and located opposite to the holder support device 5. A specimen exchange device 10 having an exchange rod 10a for transporting the specimen holder 4 into the microscope column 15 is mounted in the specimen exchange chamber 9. The inside of the microscope column 15 and the inside of the specimen exchange chamber 9 can be pumped down to a given degree of vacuum by vacuum pumping systems (not shown).
One example of the transmission electron microscope constructed in this way is described, for example, in Japanese Patent Laid-Open No. H11-185686.
With the transmission electron microscope 1 having the construction described above, the specimen 3 held on the specimen holder 4 is observed under given conditions. This is hereinafter referred to as the first observation. Then, the specimen 3 may be rotated through a given angle (e.g., 90°) and observed again. This is hereinafter referred to as the second observation.
When the first observation is performed, the specimen holder 4 on which the specimen 3 is held is first transported to a front-end portion of the exchange rod 10a of the specimen exchange device 10 mounted within the specimen exchange chamber 9. Thereafter, the specimen exchange device 10 is manually manipulated by the operator to move the front-end portion of the exchange rod 10a into the microscope column 15. As a result, the specimen holder 4 at the front-end portion of the rod 10a is transported into the microscope column 15. Inside the column 15, the holder is moved onto the support portion 5a of the holder support device 5 and held there. Then, the exchange rod 10a of the specimen exchange device 10 is pulled back, and the front-end portion of the exchange rod 10a is returned into the specimen exchange chamber 9. Subsequently, within the microscope column 15, the electron beam 12 is directed at the specimen 3 under given conditions and the first observation is performed.
After carrying out the first observation, the second observation is made as follows. First, the specimen exchange device 10 is manipulated to move the front-end portion of the exchange rod 10a into the microscope column 15. In this column 15, the specimen holder 4 supported on the support portion 5a of the holder support device 5 is transported onto the front-end portion of the exchange rod 10a. Then, the rod 10a is pulled back, and the front-end portion of the rod 10a is returned into the specimen exchange chamber 9. Thus, the specimen holder 4 on which the specimen 3 is held is moved to the exchange rod 10a of the specimen exchange device 10 from the support portion 5a of the holder support device 5 and transported into the specimen exchange chamber 9.
Then, the specimen holder 4 at the front-end portion of the exchange rod 10a is taken to the outside of the instrument from the specimen exchange chamber 9. Outside the instrument, the specimen 3 is released from the specimen holder 4 that has been taken out of the specimen exchange chamber 9. The specimen 3 is rotated through a desired angle in the specimen holder 4 by manual manipulation of the operator. Then, the specimen 3 is again held by the specimen holder 4. Under this condition, the specimen holder 4 holding the specimen 3 is inserted from outside the instrument into the specimen exchange chamber 9 and moved onto the front-end portion of the exchange rod 10a inside the exchange chamber 9.
The specimen holder 4 holding the rotated specimen 3 is then moved onto the support portion 5a of the holder support device 5 inside the microscope column 15 by the same procedure as the foregoing and supported there. The second observation is made.
An example of the prior art specimen holder 4 is shown in FIGS. 11 and 12. FIG. 11 is a plan view of the specimen holder 4. FIG. 12 is an exploded view of the holder 4, showing its structure.
As shown in FIG. 11, the prior art specimen holder 4 has a holder body 101 and a screw 103 (ring with external threads) for holding the specimen 3 onto the holder body 101.
As shown in FIG. 12, the holder body 101 of the specimen holder 4 is provided with a hole 101a for receiving and holding the specimen 3 therein. A step surface 101b is formed inside the hole 101a. The specimen 3 is received in the hole 101a formed in the holder body 101 and supported by the step surface 101b in the hole 101a. The specimen 3 is held inside the hole 101a in the holder body 101 by screwing the screw 103 into the hole 101a via a washer 102 having an opening 102a. The screw 103 is provided with an engaging opening 103a for rotating the screw 103. The screw 103 can be rotated after inserting a tool (not shown) for rotation such as a wrench into the engaging opening 103a. The outer surface of the screw 103 is threaded. The inner surface of the hole 101a formed in the holder body 101 is also threaded. The screw 103 is screwed into the hole 101a in the holder body 101 such that the threads on the screws fit over each other.
Where the second observation is made using the holder body 101 of the construction described above, the screw 103 of the holder body 101 is rotated in the direction to release the screw 103 after the end of the first observation. The screw is taken out of the hole 101a in the holder body 101. Then, the washer 102 is removed. Consequently, the specimen 3 is released inside the hole 101a of the holder body 101.
Then, the specimen 3 is rotated through a given angle inside the hole 101a of the holder body 101 by manual operation of the operator. At this time, the ti
of a tool such as tweezers is brought into contact with the surroundings of the specimen 3. The tool is rotated and thus the specimen 3 is rotated. After manually rotating the specimen 3, the screw 103 is screwed and mounted into the hole 101a in the holder body 101 via the washer 102. Thus, the rotated specimen 3 is held in the hole 101a of the holder body 101. As a consequence, the specimen 3 that has been rotated through the given angle is held on the specimen holder 4.
The specimen holder 4 on which the rotated specimen 3 is held is moved and supported onto the support portion 5a of the holder support device 5 inside the microscope column 15. Then, the second observation is made.
When the second observation is made, if the specimen 3 is rotated by manual operation of the operator as described above, the screw 103 is taken out of the hole 101a in the holder body 101 whenever the specimen 3 is rotated. Then, the specimen holder 4 is disassembled. The specimen is rotated through a given angle. Then, the screw 103 is mounted into the hole 101a in the holder body 101. In this way, these operations are repeated. Much labor and time have been required. Hence, the efficiency is not high.
Furthermore, where the specimen 3 is a biological specimen, for example, the specimen holder 4 holding the specimen 3 therein may be cooled down to below −160° C., for example, to cover the specimen with non-crystalline ice having high transparency. Then, the specimen in a frozen state may be observed. In this case, the first observation is made while the specimen holder 4 is frozen together with the specimen 3. If the specimen holder 4 is then taken out of the instrument from the specimen exchange chamber 9 to rotate the specimen 3, the frozen specimen 3 and specimen holder 4 will be exposed to the atmosphere. The moisture in the atmosphere may frost the specimen 3. If the specimen 3 is once frosted in this way, the frost will remain on the specimen when the specimen 3 is transported into the microscope column 15 through the specimen exchange chamber 9 and the second observation is made. This makes it impossible to perform appropriate observations.
If the specimen 3 is rotated within a nitrogen ambient, for example, without exposing the specimen holder 4 to the atmosphere after the specimen holder 4 is taken out of the specimen exchange chamber 9, the possibility that the frozen specimen 3 is frosted decreases. However, if the temperature of the specimen 3 increases from −160° C. while the specimen 3 is being rotated, the ice that covers the specimen 3 may vary from non-crystalline to crystalline state. If the ice that covers the specimen 3 is crystallized, the transparency of the ice deteriorates, making it impossible to perform appropriate observations.